An eccentric worm pump as used for instance for pumping medicines, foodstuffs, dyes, and the like, typically has a tubular stator extending along a main axis and having an intake side and an output side, an eccentric worm fitting in the stator and centered on a rotor axis offset from the main axis, an intake housing forming an intake compartment opening into the intake side, and a connecting shaft extending along the main axis from the rotor through the intake compartment. A drive shaft extends along the main axis from the connecting shaft out of the intake compartment through a seal housing mounted on the intake housing and sealing around the drive shaft. A drive motor connected to the drive shaft rotates the drive shaft, connecting shaft, and rotor about the axis to draw fluid through the stator from the intake side to the output side thereof.
As the worm, which typically is formed with a rounded helicoidal ridge that fits with a complementary inwardly open groove of the stator, is centered on an axis offset from the main axis, it must in effect orbit about the main axis as it is rotated. Thus it is necessary to provide a universal or cardan joint at each end of the connecting shaft, connected on the downstream side to the rotor and on the upstream side to the drive shaft, to allow such movement of these parts which are all typically made of steel. These joints must be protected by flexible cuffs.
As a result such a pump is a very complex and expensive piece of equipment. While first costs are very high, when one of the couplings or its cuffs fails, repair costs are also quite elevated.